<!DOCTYPE html>
<html lang="en">

<head>
    <title></title>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
        .container {
            
            position: relative;
            height:30vw;
            width: 30vw;
            margin: 0;
            border: 1px solid gray;
        }
        .box {
            position: absolute;
            top: 15vw;
            width: 60px;
            height: 60px;
            left: 15vw;
            margin-top: -30px;
            margin-left: -30px;
            background-color: gray;
        }
    </style>
</head>

<body>
    <div class="container">
        <div class="box"></div>
    </div>
</body>

</html>